Carb. Jetting using an A/F gage

[XR250]

I need to adjust the jetting on a new build for a 125cc Honda Navi. Started as 110cc and added a cam, pipe and carb and bore. I just installed an A/F gage on it.
If for example, it says I am at 11:1 at WOT, and am running a 110 Main jet, should I try a 11/12.5 x 110 = 98 (say 100) main jet assuming I want 12.5:1 as my target mixture?
Also, is 12.5 a good number for WOT? What should I be shooting for a low and mid throttle?


Thanks

 

[XR250]

There might be something found in tailoring the length of that runner to the operating RPM of the engine.

Maybe but not enough motivation here for that

 

[XR250]

So after many permutations of jetting and sanding the carb needle, I am back to the stock carb needle dropped as low as it will go, a 32 pilot, 115 main.
Idle, midrange and WOT are all about perfect with 14.5:1, 13.5:1 and 12.6:1 respectively. 1/8 ish throttle is lean running 15-16 AFR. It runs OK in this range and it is about 30 mph so i am here a lot. Is it going to damage the engine at this low load due to lean overheating? I can try a new needle and just lightly sand it to get the ratio better in this range but I do not mind how it runs now.
I think I saw a dyno pull of a new Honda XR150 and it was in the 17's at part throttle.

 

[gruntguru]

15-16 is fine. As long as it has enough spark advance that AFR will give best economy.

 

[XR250]

15-16 is fine. As long as it has enough spark advance that AFR will give best economy.

Well, I'll hope so as i have no control over that! My new ECU comes in a few days but the only adjustment is rev limit.
Thanks

 

[mfgenggear]

How does this apply to my original post?

The timing will affect performance, may or may not be the case here. Due to regulations oem will retard timing. , if it is timing will require correction.
Type of carburetor same deal an after market
May or may not improve performance.

Stock carburetors can be a pita. Can have bad performance.

AF gage are great. But part of getting good flow is porting of the head. Increasing air flow , increase fuel. And mixture. Polishing and porting carefully.

Looking at confirming what the AF gage is reading. Running lean is really bad, but running rich can carbon up components. Can cause sticking valves, carbon up the piston, over compress the cylinder. Causing head gasket failure.